The present invention relates generally to apparatus and methods for forming individual foam-filled bags commonly used as protective cushions in the packaging arts. More particularly, the present invention relates to apparatus and methods for forming such protective cushions by dispensing two streams of reactive foam components between opposing panels of a flexible sheet material and mixing the streams together therebetween in order to produce an expandable foam between the panels.
In the packaging industry, expandable foams have been used for some time to form protection for packaged articles. Conventional practice in such industry has included filling a cardboard box with an expandable foam, such as a urethane or polyurethane foam, and contacting the foam with a plastic barrier sheet to create a protective cushion and then placing an article for shipping into the box on the cushion. The article may then also be covered with another plastic sheet and a second filling of expandable foam accomplished before closing the box.
Another practice in the industry utilizes foam cushions which are inserted into the packing box immediately after the foam cushions are made. This is accomplished by machines which react two foam components together in a gun apparatus and then dispense the foam so formed between two opposing plastic sheets, and seal the edges to form a protective foam cushion. Numerous patents exist which describe such methods and apparatus. Two such patents, U.S. Pat. No. 4,999,975, issued Mar. 19, 1991 and U.S. Pat. No. 4,800,708, issued Jan. 31, 1989 describe apparatus for foam cushion making in which a foam dispenser, or gun, is positioned between two opposing plastic panels. Two different reactive foam components, commonly referred to as foams precursors, are mixed together in the foam gun in order to form the foam, which is then dispensed under pressure between the two opposing plastic panels to form the foam protective cushions.
Although such apparatus and methods are operational and produce protective foam cushions which adequately provide protection to packaged articles, they are not without certain inherent disadvantages. For example, they reply upon a mixing chamber or cartridge in the foam gun to provide an area wherein the foam components are mixed together to form the expandable cushioning foam. Once formed, the foam is then dispensed under pressure through a nozzle downstream of the mixing chamber. The mixing chamber typically accumulates hardened foam over time and thus must be cleaned at regular intervals, typically at weekly intervals. The apparatus must then be taken apart to be cleaned, thereby leading to detrimental downtime of the apparatus.
Other apparatus rely upon a complex foam dispensing gun structure which utilizes two ports to convey the two reactive foam components to a mixing chamber preceding the dispensing end of the gun. In this type apparatus, the mixing chamber may include a valving rod which slides in and out of the mixing chamber to control the flow of at least one of the reactive foam components. This type of apparatus is also not without certain disadvantages, for although the valving rod effectively acts as a valve to control the flow of the reactive foam components into the mixing chamber, the foam formed by the reactive components has been known to slowly build up in the mixing chamber and on the valving rod itself. Additionally, when a valving rod is used, "crossover" between the foam components may occur when one of the foam components accumulates on the valving rod and makes contact with into the other foam component as the valving rod slides back and forth to form a reacted, hardened foam. The valving rod then must be cleaned, which typically requires scraping the accumulated foam off of the valving rod. Each cleaning wears down the tolerance of the rod to eventually wear down the overall effectiveness of the foam dispensing gun of these devices.
In order to prevent the buildup of foam in the mixing chamber and dispensing nozzles of the aforementioned apparatus, solvent systems which continuously dispense solvents through the foam dispensing systems used therein in order to maintain them in a clean state. These solvent systems increase the complexity and cost of the apparatus.
The present invention is directed to an apparatus and methods for producing foam cushions which overcomes these disadvantages.